A SubmarinePatent is a patent which an "inventor" files on a device or technology that doesn't exist yet, or which has not yet been successfully implemented. Using various procedural mechanisms, the filer intentionally delays issue of the patent, sometimes for years, until a practical implementation of the device/technology appears on the market. At that time, the filer allows the patent to "come to the surface" and demands royalties from the party who did the real work.

In the US, until recently, patents lasted 17 years from the date of issue - so a submarine patent could lurk under the surface for many years until an infringing product did appear. Recently, the US went to 20 years from date of filing. This reduces the scope of submarine patents by preventing filers from indefinitely delaying the issue of their patents. It does not prevent submarine patents in general, since one can still file a patent on a technology that has not been fully implemented and collect royalties from the real implementor; however, a patent filed in 2003 will expire in 2023 no matter when it issues, so the filer can benefit from the submarine patent only for a fixed period of time, far shorter than under the old system.

For example, under the old system, someone in 1950 could have filed a patent on, say, a packet-based computer network router, though there were as yet hardly any computers to speak of. By requesting repeated "continuations" during the patent application process, the filer could force the patent to be delayed indefinitely until packet-based routers started to come onto the market, say in 1970. The filer then stops requesting continuations, the patent issues, and the patent-seeker can collect royalties on network routers for 17 years from that point, until 1987.

Under the new system, a patent filed in 2003 will expire in 2023 no matter when it issues. So if someone were to file a patent on a time machine (I'm sure it has been tried) today, and it doesn't get invented by 2023, said patent-filer is out of luck. If the time machine were to be invented before 2023 in this example, the patent holder might still get royalties, but for far shorter a time than under the old system.

But you can't file a patent on a time machine - as soon as you use it to go back in time, you establish prior art and break your own patent! Yes, most of patent law would probably have to go out the window at that point.

A truly horrid loophole in the patent law? You bet. But SubmarinePatents have been repeatedly upheld by the courts as valid (often with the judge stating "this stinks, but the law is the law...")
A submarine patent was one that the inventor deliberately kept from granting by creating office actions, so that (especially for obvious inventions) other people derived the same invention and then when the patent granted, they are in infringement with a shipping product.

Submarine patents are no more. You can't keep a patent application from surfacing for more than a year in the US now.

[I think that is 18 months.]
Submarine patents still exist. Although you can't prevent a patent from being publicly disclosed, who has time to review the millions of claims in all the patents that get issued. Surely some submarine patents are still sneaking through the complicated process. Anyway, I define submarine patent as any patent that you get that you don't intent do implement yourself. I know, many companies are calling them "Defensive Patents", but that's just a marketing word for "Submarine Patent".
Us Patent Office

I've often wondered if fighting these kinds of patents would cost more than, say, a professional killer? Might it not make sense to use violence to solve the patent case? The LawOfDepletingPrinciples.
See: BlackBoxJerry